1. Field of the Invention
The present invention relates to a transparent laminate excellent in impact resistance which is suitably used as for example a bulletproof face guard, bulletproof shield, a glazing member of various vehicles, a partition board on a bank counter, a crime preventive door and the like.
2. Description of the Related Art
A transparent plate having impact resistance is often used as a glazing member in public facilities, athletic facilities and the like, as a partition board on a bank counter and the like, as a glazing member of a crime-preventive door and the like, as a glazing member of various vehicles, as well as for other materials and applications.
As such a transparent plate, there are known silicate glass plates, polycarbonate-based resin plates, and further, a transparent laminate obtained by bonding a silicate glass plate to a polycarbonate-Dased resin plate via a methacrylate-based syrup (USP 4,125,669), transparent laminates obtained by bonding a plurality of polycarbonate-based resin plates via an adhesive layer composed of a thermoplastic polyurethane-based resin (GB 1498265, Japanese Patent Application Laid-Open(JP-A) Nos. 4-301448, 4-361034), and the like. However, in these transparent plates, there is a problem that for improving impact resistance, an increase in thickness is required, and consequently their weight increases, which often leads to a lack of practicability.
For solving such a problem, there have been suggested transparent plates obtained by bonding an acrylic resin plate to a polycarbonate-based resin plate via an adhesive layer (USP 5,773,139). By these means, it has become possible to secure impact resistance while at the same time maintaining light weight.
However, in the above-described prior technologies, when the plate receives an impact several times repeatedly, the impact resistance thereof is not satisfactory. Namely, though a protective ability against a strong impact can be manifested sufficiently, when the plate receives an impact several times, particularly when the plate receives an impact several times at the same position, small fragments are often scattered from parts around the impact position with such small fragments being deleted from the impact position of the transparent plate, to thereby cause the possibility of a decrease in visibility through the impact position. Such a deletion of small fragments is not preferable, with respect to the appearance of the product when the product is going to be used continuously.
In view of such background considerations, there has been desired the development of a transparent plate having a sufficiently improved impact resistance in the case of being impacted several times repeatedly, without sacrificing or losing properties such as light weight, transparency and the like.
An object of the present invention is to provide a transparent laminate which is light and excellent in transparency and which can manifest a sufficient protective ability against strong impact, and which is excellent in impact resistance when subjected to repeated impacts.
For attaining this object of the invention, the present inventors have intensively studied and found that impact resistance against repeated impacts can be improved while maintaining light weight and transparency, by the integrated bonding of (i) a surface layer composed of a polycarbonate-based resin via a surface bonding layer composed of an acrylic resin, to (ii) a first substrate of a laminated substrate structure, which laminate substrate structure is obtained by bonding the first substrate composed of an acrylic resin to a second substrate composed of a polycarbonate-based resin via a first bonding layer composed of a resin layer having a glass transition temperature(Tg) of about 50xc2x0 C. or less, and that warping of the laminate comprising the surface layer, the surface bonding layer and the first substrate is decreased by further laminating a third substrate composed of a polycarbonate-based resin between the first substrate and the second substrate, by bonding the third substrate via a second bonding layer composed of a acrylic resin, with the third substrate also being bonded to the second substrate via the first bonding layer.
Namely, in a first embodiment of the invention, the transparent laminate of the present invention comprises a laminate substrate obtained by bonding a second substrate composed of a polycarbonate-based resin to a first substrate composed of an acrylic resin via a first bonding layer composed of a resin having a glass transition temperature (Tg) of about 50xc2x0 C. or less, and a surface layer composed of a polycarbonate-based resin bonded via a surface bonding layer composed of an acrylic resin to an outter surface of the above-described first substrate. (See FIG. 1)
In a second embodiment of the above-described transparent laminate, a third substrate composed of a polycarbonate-based resin is laminated between the first substrate composed of an acrylic resin and the second substrate composed of a polycarbonate-based resin, such that the third substrate is bonded to the first substrate via a second bonding layer composed of an acrylic resin, and the third substrate is bonded to the second substrate via the first bonding layer respectively. (See FIG. 2)